Make DiagnosticIDs::getAllDiagnostics use std::vector. NFC.

The size of the result vector is currently around 4600 with
Flavor::WarningOrError, which makes std::vector a better candidate than
llvm::SmallVector.

Patch by: Andras Leitereg!

Differential Revision: https://reviews.llvm.org/D39372

llvm-svn: 321190
diff --git a/clang/lib/Basic/DiagnosticIDs.cpp b/clang/lib/Basic/DiagnosticIDs.cpp
index 5c53f35..c4c425d 100644
--- a/clang/lib/Basic/DiagnosticIDs.cpp
+++ b/clang/lib/Basic/DiagnosticIDs.cpp
@@ -583,7 +583,7 @@
 }
 
 void DiagnosticIDs::getAllDiagnostics(diag::Flavor Flavor,
-                                      SmallVectorImpl<diag::kind> &Diags) {
+                                      std::vector<diag::kind> &Diags) {
   for (unsigned i = 0; i != StaticDiagInfoSize; ++i)
     if (StaticDiagInfo[i].getFlavor() == Flavor)
       Diags.push_back(StaticDiagInfo[i].DiagID);